1. Field of the Invention
The present invention relates to a controller for an electrical power steering apparatus.
2. Description of the Related Art
It is well known in the prior art of a motor driving apparatus in which a switching element of a MOS-FET is mounted in a conducting path between a battery and a motor driving circuit to drive a motor by controlling the conduct to the motor by the way of turning on or off the MOS-FET in accordance with various causes. The motor driving apparatus is popular for a controlling circuit of the various kinds of the motor.
There happens an on-fault or a off-fault of the MOS-FET as the switching element on a basis of various causes in the prior art. Because of that, the previous apparatus detects the fault of the MOS-FET as a short fault or an open fault by judging whether the MOS-FET is in an ON stage or not as disclosed in the Japanese Patent Tokkai 2008-141612.
In general, a controller for a power steering as a prior art includes a MOS-FET as a switching element to turn on or off the conduct of the power. However, a parasitic diode is mounted at a reversed direction between a drain and a source of the MOS-FET, for example so that the current is flown in a direction from the drain to the source at a N-channel MOS-FET. According to this construction, the fault of the MOS-FET can not be detected because the current is flowing to continue its operation where the parasitic diode is on as a normal.